Hi all,
I'm quite new to audio and all. For my study I'm currently looking into a set up, which we want to modify.
The current set-up consists of a loudspeaker, pneumograph (measures pressure and flow) and a mouthpiece. The mouthpiece is designed for tidal breathing so that the vibrations generated by the loudspeaker are superimposed over the breathing. This gives information about the lung properties. This is visualized here. The set up is connected to a computer via a box with probably an AD converter and...? The current setup is controlled from software and in which no adjustments of the signal possible is.
We want to be able to determine the amplitude and frequency of output signal ourselves and then also process the signal of what has been measured by the pneumograph. That's why we want to adjust the hardware of the setup.
It is the intention that everything can be controlled and read via MATLAB. The sound waves must have a frequency range of 5-100Hz and an amplitude of 10-15 cmH2O (300-500 Pascal in an open tube and 1000-1500Pa with a patient attached (closed tube with resistance at one side and patient at the other side). (this factor of 3 already exists in the current set-up (although I'm unsure if it remains linear)). These are approximately 10 times higher amplitudes than in the current set-up
Because I am fairly new to the sound domain myself, I would like tips on how I can best create such a new set-up cost-efficiently. What equipment would you recommend?
Would you continue to work with the old analog speaker (which already is used in another project to create waves with the intended amplitudes) and connect an amplifier to magnify te signals, or would you use an oscilloscope in combination with the same old speaker. Another option might be to replace the analog speaker with a digital one with an internal amplifier? The current analog speaker has a db9/com port as output.
I think that especially the low frequency range is a point of attention. So what equipment would be sufficient for this?
Someone advised a class D amplifier. But I did not fully understand what the disadvantages are. Something about a DC offset that could damage the speaker. Can somebody help me to understand the basics of that?
Complicated question, but I hope someone can help me. Thanks in advance!
I'm quite new to audio and all. For my study I'm currently looking into a set up, which we want to modify.
The current set-up consists of a loudspeaker, pneumograph (measures pressure and flow) and a mouthpiece. The mouthpiece is designed for tidal breathing so that the vibrations generated by the loudspeaker are superimposed over the breathing. This gives information about the lung properties. This is visualized here. The set up is connected to a computer via a box with probably an AD converter and...? The current setup is controlled from software and in which no adjustments of the signal possible is.
We want to be able to determine the amplitude and frequency of output signal ourselves and then also process the signal of what has been measured by the pneumograph. That's why we want to adjust the hardware of the setup.
It is the intention that everything can be controlled and read via MATLAB. The sound waves must have a frequency range of 5-100Hz and an amplitude of 10-15 cmH2O (300-500 Pascal in an open tube and 1000-1500Pa with a patient attached (closed tube with resistance at one side and patient at the other side). (this factor of 3 already exists in the current set-up (although I'm unsure if it remains linear)). These are approximately 10 times higher amplitudes than in the current set-up
Because I am fairly new to the sound domain myself, I would like tips on how I can best create such a new set-up cost-efficiently. What equipment would you recommend?
Would you continue to work with the old analog speaker (which already is used in another project to create waves with the intended amplitudes) and connect an amplifier to magnify te signals, or would you use an oscilloscope in combination with the same old speaker. Another option might be to replace the analog speaker with a digital one with an internal amplifier? The current analog speaker has a db9/com port as output.
I think that especially the low frequency range is a point of attention. So what equipment would be sufficient for this?
Someone advised a class D amplifier. But I did not fully understand what the disadvantages are. Something about a DC offset that could damage the speaker. Can somebody help me to understand the basics of that?
Complicated question, but I hope someone can help me. Thanks in advance!
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1Pa is 94dB SPL, so 10kPa is 174dB SPL
This is very strong subbass. The acoustics of the set up are unique, I think you are going to be doing some experimental testing and calibration, and in particular I suspect you have resonances that are highly variable.
Jumping up 20dB in power levels brings immediate safety concerns - 100 times more power in infrasound system means 100 times the destructive power. That worries me, infrasound can kill.
This is very strong subbass. The acoustics of the set up are unique, I think you are going to be doing some experimental testing and calibration, and in particular I suspect you have resonances that are highly variable.
Jumping up 20dB in power levels brings immediate safety concerns - 100 times more power in infrasound system means 100 times the destructive power. That worries me, infrasound can kill.
You are right. I think I messed up my units. I thought the graph I used for reference had Pa as unit. However, on second thoughts, this can not be the case. The pressure during quiet breathing should be around 1cmH2O, which equals 100 Pa and increases up to 15 cmH2O during heavily breathing, which should equal 1500 Pa. The waves we want to create should have similar or a bit smaller amplitudes.
I will adapt this in the initial post.
I will adapt this in the initial post.
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Please work with someone who knows this stuff.
Sound waves in normal life are much-much-much-much-much-much-smaller than atmospheric pressure. Yes breathing pressure variations are less than atmospheric but likely far less than typical (safe?) sound pressure variations. I also don't think you really want to measure with an unusually large superimposed pressure variation on the lung's normal pressures, unless you really plan to stress the lung.
Note that tympanometry does a similar test on the ear, measuring ear volume and compliance. There is no huge pressure transducer or stress on the ear. Maybe a study of tympanometry will guide your lung study.
Sound waves in normal life are much-much-much-much-much-much-smaller than atmospheric pressure. Yes breathing pressure variations are less than atmospheric but likely far less than typical (safe?) sound pressure variations. I also don't think you really want to measure with an unusually large superimposed pressure variation on the lung's normal pressures, unless you really plan to stress the lung.
Note that tympanometry does a similar test on the ear, measuring ear volume and compliance. There is no huge pressure transducer or stress on the ear. Maybe a study of tympanometry will guide your lung study.
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I'm working with a pulmonary physiologist, so he can make sure we will not use too high pressures. Moreover, I also contacted a technician to help me build te construction.
As reference: During mechanical ventilation pressures up to 30 cmH2O can be used. We will only use pressures that are smaller. Moreover, we do not intent to immediately use the maximum pressures that I mentioned. We want to slowly increase the pressure to a safe, but sufficient pressure. A hospital technician will check the safety of the set up. Not all frequencies will have a large amplitude and possibly only frequencies up to 40 Hz will be used. The lowest frequency will probably have the relatively largest amplitude and the others will be small deviations from that, keeping the total amplitude within a safe range. The pressures I mentioned would be the maximum of the possible total amplitudes and probably won't be used. However, I mentioned those, so the equipment will have a sufficient range.
So, based on making sure everything is safely executed under supervision that has more knowledge about the safety concerns. How would you advice me to amplify the original pressure wave?
As reference: During mechanical ventilation pressures up to 30 cmH2O can be used. We will only use pressures that are smaller. Moreover, we do not intent to immediately use the maximum pressures that I mentioned. We want to slowly increase the pressure to a safe, but sufficient pressure. A hospital technician will check the safety of the set up. Not all frequencies will have a large amplitude and possibly only frequencies up to 40 Hz will be used. The lowest frequency will probably have the relatively largest amplitude and the others will be small deviations from that, keeping the total amplitude within a safe range. The pressures I mentioned would be the maximum of the possible total amplitudes and probably won't be used. However, I mentioned those, so the equipment will have a sufficient range.
So, based on making sure everything is safely executed under supervision that has more knowledge about the safety concerns. How would you advice me to amplify the original pressure wave?